1. Field of the Invention
The present invention relates generally to a power control system of a vehicle such as a passenger car, a truck or the like, and more particularly to the system for controlling power generation of an alternator according to conditions of a battery in the vehicle.
2. Description of Related Art
To detect the electric current flowing through a battery and the battery voltage, a current sensor and a voltage sensor have been used. Further, to detect malfunctions of the sensors, a sensor malfunction detecting device is well known. This device is, for example, disclosed in Published Japanese Patent First Publication No. 2003-68366. In this device, a data processing unit is used only for detecting a malfunction of the current sensor and a malfunction of the voltage sensor, and a display notifies the occurrence of the malfunction.
Further, to control a quantity of electric power generated in an alternator mounted on a vehicle, an alternator controlling device is known. This device is, for example, disclosed in Published Japanese Patent First Publication No. 2007-97336. In this device, a temperature sensor detects the battery temperature, and an electronic control unit (ECU) controls electric power generated in the alternator according to the battery temperature. When the ECU detects a malfunction of the temperature sensor, a display such as a warning lamp is switched on under control of the ECU to notify the occurrence of the malfunction.
However, in the alternator controlling device and the malfunction detecting device, to notify the occurrence of a malfunction, it is required to additionally install a display in an instrument panel. Therefore, the area of the panel for on-board installation is undesirably increased, and the manufacturing cost of the device is increased.
To avoid the additional installation of a display notifying malfunctions of various sensors, it is thinkable to use a single alarm as the combination of a display (e.g., a warning lamp notifying insufficient power generation) notifying a malfunction of an alternator and another display notifying malfunctions of various sensors. However, in this case, it is required to additionally install an electric circuit for producing an alarm signal and inducing the alarm to output the warning sound in response to the alarm signal. Therefore, the manufacturing cost of the device is undesirably increased.
Further, when a judgment on a malfunction of each of various sensors is performed independent from a judgment on a malfunction of an alternator to output a warning indicating the occurrence of a malfunction in one of the sensors or the alternator, the precision in the judgment is sometimes lowered. For example, even when the electric power supplied to the battery is sufficient, the device undesirably outputs a warning indicating that the voltage of electric power generated in the alternator is low. When the device is set so as to excessively heighten sensitivity in the judgment, the device frequently outputs unnecessary warnings. In contrast, when the device is set so as to excessively lower sensitivity in the judgment, the device sometimes output no warning even when the output voltage of the alternator or the battery voltage is excessively lowered so as to require a warning.